3. Premedication --> Maintenance of Anesthesia Flashcards
benzodiazepine drugs
midazolam (versed)
lorazepam
diazepam
benzodiazepine mechanism
binds to GABA receptor
benzodiazepine effects
anxiolysis
antegrade amnesia
anticonvulsant
minimal cardiac/resp depression
benzodiazepine reversal agents
flumazenil (Romazicon)
benzodiazepine side effects
increased apnea
increase risk of post-op cognitive dysfunction
midazolam administration
IV
PO
intranaal
midazolam IV dose
1-2mg
midazolam PO (peds)
0.3-0.7 mg/kg
up to 20mg
midazolam intranasal dose
0.2-0.5mg/kg
causes nasal burning
midazolam onset IV
rapid
20-25 secs
midazolam onset PO
10-15 min
midazolam onset intranasal
5-10 min
Pre-Induction Checklist
Machine
Suction
Monitors
Airway (+emergency devices)
Invasive lines
Drugs
Special items
most common methods for inducing pt
IV
Mask
IM (ketamine dart)
fresh gas flow (FGF)
how fast gas is flowing
(L/min)
Inspiratory concentration factors
(Fi)
Fresh gas flow
breathing circuit volume
circuit absorption of agent
when machine absorbs a high amount of agent…
the pt absorbs less agent
FGF and Fi relationship
directly proportional
FGF and circuit volume relationship
???
increase volume decrease delivery?
alveolar concentration factors
(FA)
uptake (into blood)
minute ventilation
overpressurization
we want FA to ______
increase as quickly as possible
uptake (into blood)
incr uptake decr partial pressure
uptake factors
blood:gas coefficient
pulmonary blood flow
difference in alveolar gas and blood
blood: gas coefficient
tells us how soluble an agent is in the blood
more soluble = more uptake
= slower FA increase
high B:G
slower FA increase
low B:G
faster FA increase
pulmonary blood flow
decreased CO = decreased uptake
= faster FA
agent concentration in alveolar gas vs venous blood
want higher [agent] in aveoli vs blood
generates larger driving force
N2O B:G
0.47
Iso B:G
1.4
Des B:G
0.42
Sevo B:G
0.65
minute ventilation and FA relationship
increased minute ventilation replaces anesthetic taken up into pulmonary
we want higher minute ventilation
overpressurization effect
increase amt of agent inspired (Fi)
increase Fi = increased downstream concentration
Fi vs FA
increasing Fi leads to a greater increase FA
5x Fi = 6.2x FA
augmented inflow effect
add gas to replace absorbed agent
Patm > Palveoli
sucks gas into alveoli (high – > low)
5xFi = 6.8x FA
second gas effect
soluble first gas (N2O) is given at high inspired concentrations
N2O leaves alveoli quickly
causes over pressurization of sevo
increases driving factor
==faster induction
the partial pressure of the gas left behind (sevo) is relatively greater than that of the remaining gases (over pressurization)
Arterial concentration (Fa) factors
Ventilation-Perfusion mismatch (V/Q)
ventilation-perfusion mismatch
(V/Q)
mismatched distribution of ventilation / perfusion of lung units
some receiving high ventilation
others receiving high perfusion
V/Q results in
alveolar dead space
incr deadspace
== decr induction speed
Procedures that may cause V/Q
bronchial intubation
R-L shunt
MAC
the end-tidal concentration necessary to prevent movement in 50% of pts
1.3 MAC
prevents movement in 95% of surgical pts
(1.2-1.3 MAC)
0.5 Nitrous + 0.5 Sevo =
1.0 MAC
MAC is additive
MAC-awake
end tidal concentration that allows pt to respond meaningfully to stimuli
0.3-0.5 MAC
MAC-Awake (N2O)
0.64 MAC
MAC - Amnesia
concentration to prevent recall in 50% of pts
0.25-0.4 MAC (up to 0.6)
MAC-BAR
concentration where 50% of population wont mount an adrenergic response
1.5-1.6 MAC
N2O MAC
105%
ISO MAC
1.2%
DES MAC
6.0%
SEVO MAC
2.0%
MAC and age relationship
inversely proportional
young age = higher MAC
N2O supports…
combustion
N2O –> 2N2 + O2
what gas agent does not trigger MH
N2O
N2O cardiovascular response
sympathomimetic
no change to HR (slight evelation)
N2O respiratory response
increase RR
decrease TV
increase PVR (pulm vasc. resistance)
N2O mechanism
NMDA receptor antagonist
may provide analgesia bc NMDA is involved in pain transmission
N2O contraindications
N2O will expand air filled spaces
Sevo properties
nonflammable
non-pungent
Sevo CV effects
decrease contractility
decrease SVR
decrease BP
no change HR
Sevo respiratory effects
increase RR
decrease TV
bronchodilator
Sevo cerebral effects
increase CBF
increase ICP
decrease CMRO2 (brain O2 consum)
Sevo and MH
triggers MH
Sevo metabolism
5% metabolized
flouride metabolite - nephrotoxicity
Compound A
produced by interactions w/Sevo and the barium hydroxide lime/soda lime
nephrotoxic
2LPM flow rate for sevo gas
Isoflurane properties
nonflammable
Iso CV effects
decrease contractility
decrease
SVR
decrease BP
increase HR
maintains CO (cardiac output)
vasodilation
Iso Respiratory effects
increase RR
decrease TV
bronchodilation
Iso Cerebral effects
increase CBF
increase ICP
decrease CMRO2
ISO and MH
triggers MH
coronary steal
Pt has blocked CA == vasodilation
if you give Iso:
Iso causes vasodilation of other arteries which “steal” blood from the blocked CA
Des properties
non-flammable
pungent airway irritant
20C vapor pressure = 681mmHg
(special vaporizer)
Des CV effects
increase HR
decrease SVR
decrease BP
maintain CO
Des respiratory effects
increase RR
decrease TV
bronchoconstriction (asthmatic pts)
Des cerebral effects
increase CBF
increase ICP
decrease CMRO2
Des and MH
triggers MH
how do we choose volatile agent?
type of surgery
cost/availability
fat:blood ratio
pt characteristics
N2O F:B
2.3
Iso F:B
45
Des F:B
27
Sevo F:B
48
why IV induction more common?
rapidly bypass stage 2
rapid recovery after bolus dose due to redistribution to tgt site
more portable
not greenhouse gases
Propofol mechanism
GABAa receptor agonist
propofol onset
rapid
Propofol duration of action
short
why?
Propofol expiration
6 hrs post opening
Propofol CV
decrease BP
decrease SVR
decrease preload
decrease contractilioty
Propofol Respiratory
profound resp depression
depresses upper airway reflexes
Propofol Cerebral
decrease CBF
decrease ICP
decrease CMRO2
anticonvulsant (incr seizure thresh)
myoclonic movement
Proprofol misc effects
histamine release
antiemetic
Ketamine Mechanism
NMDA antagonist
Ketamine main effect
dissociative anesthesia
- diss sensory impulses from limbic cortex
- limbic system: awareness of sensation/emotions
Ketamine administration
IV
IM
Oral
Nasal
Rectal
low dose infusion for pain
Ketamine IV Onset/DOA
Onset: rapid
DOA: 5-10 min
Ketamine CV
incr BP
incr HR
incr CO
incr myocardial O2 demand
central sympathetic stimulant
(direct myocardial depressant)
Ketamine respiratory
no resp depression
bronchodilation
intact airway reflexes/muscle tone
Ketamine cerebral
incr CBF
incr ICP
incr CMRO2
Ketamine side effects
psychotomimetic (dreams/delirium)
seizures at low dose
anticonvulsant at high dose
incr secretions
Etomidate mechanism
GABA receptor agonist
depresses reticular activating system
(RAS)
- regulates sleep/arousal
Etomidate Onset
rapid
Etomidate metabolism
hepatic
plasma esteraseE
Etomidate side effects
PONV
myoclonus (30-60%)
injection pain
adrenal suppression (24-48 hrs post)
Etomidate CV effects
minimal
Etomidate Respiratory effects
mild resp depression
Etomidate Cerebral effects
decr CBF
decr ICP
decr CMRO2
maintains CPP (perfusion pressure)
increases SSEP amplitude (TOF?)
seizure potential
Lidocaine induction uses
reduce propofol burning
blunt airway response to DL
1mg/kg IV
Most common analgesic
fentanyl
fentanyl properties
fast acting
fat soluble =
crosses plasma membrane
long half life
Neuromuscular blocking agents
depolarizing
non-depolarizing
Succinylcholine mechanism
depolarizing
attached to ACh receptor causing random fasiculations and eventual paralysis
Sux onset/DOA
onset: 45 sec (IV)
duration: 10 min
Sux reversal
no reversal needed due to rapid recovery
Sux metabolism
plasma psuedocholinesterase
(butyrylcholinesterase)
Sux myalgia treatment
can treat w/ROC
(0.06-0.1 mg/kg IV)
Sux CV effects
bradycardia
(stimualtes cardiac postgang muscarinic receptors)
Sux and MH
triggers MH
Sux Contraindication
muscular dystrophy
– sux can trigger rhabdo
hyperkalemia
–sux can incr [K+] by 0.5
– burns/trauma
–spinal cord injuries
–sepsis
Pseudocholinesterase deficiency
AKA atypical plasma cholinesterase
AKA atypical Butyrylcholinesterase
genetic abnormality in psuedocholinesterase gene
Heterozygous atypical
pseudocholinesterase deficiency
20-30min blockade duration
dibucaine #: 40-60
Homozygous atypical
pseudocholinesterase deficiency
60min-8hr blockade duration
dibucaine #: 20-30
dibucaine number
test for pseudocholinesterase def
measures function not amount
less inhibitory to genetic changes
(homo: lower number)
(hetero: higher number)
(not mutated: highest)
Non-Depolarizing NMB categories
benzoisquinolone
steroidal
chlorofumarate
benzoisquinolone NMB drugs
cisatracurium
steroidal NMB drugs
vecuronium
rocuronium
chlorofumarate NMB drugs
gantacurium (experimental)
rocuronium onset/duration
onset: 60-90s
duration: 35-75 min
roc elimination
mostly biliary
some kidney
- not prolonged by kidney failure
vecuronium onset/duration
onset: 2-3 min
duration: 45-90 min
vec elimination
mostly biliary (small hepatic)
25% kidney
- mod prolong by kidney failure
cisatracurium onset/duration
onset: 2-3 min
duration: 40-75 min
cisatracurium elimination
hoffman elimination
- laudanosine metabolite
**use with kidney/liver failure pts
pH/temp sensitive drug